Means for the elimination of ripples in cascade coupled thermionic valves



Aug. 22, 1932.. E Q LOFGFQEN 1,923,222

MEANS FOR THE ELIMINATION OF RIPPLES IN CASCADE COUPLED THERMIONIC VALVES Filed July 28. 1930 //v var Patented Aug. 22, 1933 UNITED STATES PATENT OFFICE MEANS FOR THE ELIMINATION OF RIPPLES IN CASCADE C O U P L E D THERMIONIC VALVES Application July 28, 1930, Serial No. 471,295, and

in Sweden August 3, 1929 1 Claim.

The present invention has for'its object an improvement in transformer-coupled apparatus according to patent application No. 302,564.

In transformer-coupled apparatus according to 5 the main patent it may occur, especially at a.

high ratio of the transformer and a high amplification factor of the last valve, that the first valve,

upon the net ripples being compensated, receives a rather too high negative grid biasing voltage. The internal alternating current resistance of the valve will then be comparatively high which in turn afiects the operation of the apparatus detrimentally in many respects. The amplification at low frequencies is thereby reduced and the back coupling efiect in a valve operating as a detector will be considerably disturbed and, finally, the conditions will be less favourable for obtaining a satisfactory compensation of the ripples. The present invention has for its object to eliminate said inconveniences in the original circuit arrangements.

The invention simply consists therein, that a high resistance is connected into circuit between the anode of the valve preceding the last valve in the apparatus and a point of the voltage divider having a comparatively high positive voltage in relation to the cathode.

On the drawing there is shown a two-valve apparatus (an amplifier or a radio receiver) arranged according to the invention. The apparatus comprises a tuning coil, a transformer winding or the like L over which the incoming impulses are supplied to the grid of the first valve. The said high resistance is designated R.

If the resistance R. were omitted; the ripple voltage supplied to the primary winding of the transformer T would be E1=v..+m (1) where Va and Vg are the ripple voltages, referred to the cathode of the valve V1, in the points 5 and a: on the voltage divider and p. the amplification factor of said valve.

After connecting the resistance R into circuit the corresponding expression will be as follows:

where Ea is the ripple voltage, also referred to the cathode of the valves V1, in the point 6 and p the internal alternating current resistance of the valve V1.

If R is high in comparison with p the second term on the right hand side of the equation 2 will be of nearly the same value as the corresponding term in the equation 1. Said term is negative if Va is counted positive (Va and V; are tapped off from the voltage divider on opposite sides of the cathode). In addition, there will be another negative term in the Equation 2 which will be of an order of value comparable with the preceeding term, provided Ea is selected comparatively high. The ripple voltage E1, which is required on the primary winding of the transformer to compensate net ripples in a loudspeaker, may now, due to the addition of said third term, be brought about by a lower value of Vg than before which also results in a lower direct current biasing voltage of the grid. By a suitable adjustment of R and Ea the apparatus may becompensated at any grid biasing voltage of the first valve.

Regarding the other parts of the circuit arrangement, the application of phase correcting impedances etc., reference is made to the main patent.

The invention may, of course, be applied to apparatus having more than two thermionic valves. In this case the resistance R may be connected to the anode in any one of the valves preceding the last valve. If desired, the compensation circuit arrangement according to the invention may be repeated in several of the valves preceding the last valve.

I claim-' In an electric apparatus having thermionic tubes connected in cascade by means of transformers, an ohmic voltage divider connected to a direct current source, and a number of tappings from said voltage divider for the supply of anode and grid direct-current voltages to said tubes, the combination of a high ohmic resistance connecting the anode of a preceding tube with the voltage divider at a point thereof having a high positive potential in relation to the cathode of said tube, with a current path from the same anode, through the primary winding of the next cascade transformer and to the voltage divider at another point thereof having also a high positive potential in relation to said cathode but a les potential than the former point.

ERIK OLOF LOFGREN. 

